This invention relates to automatic transmissions having a layshaft kinematic arrangement, particularly to automatic transaxles having dual input clutches, but no torque converter.
Automatic transmissions for transmitting power between an input and an output, either over a continuously variable range of speed ratios or in discrete step changes among speed ratios, have associated with them several sources of parasitic losses, which adversely affect fuel economy. These losses are associated with a torque converter, open hydraulic friction clutches and brakes, hydraulic pump, and gear meshes.
To improve fuel economy in a motor vehicle having an automatic transmission, an automated shift manual (ASM) transmission can be used to eliminate or substantially reduce all of these parasitic losses except gear mesh losses. An ASM transmission generally performs gear ratio changes by first interrupting torque transmitted from the engine to the transmission input, preparing the transmission components associated with the next speed ratio, and then restoring torque at the input. A primary functional feature of ASM transmissions is the need to interrupt power transmitted from the engine to the transmission input shaft before or during each gear ratio change.
Dual clutch layshaft transmissions are essentially two ASM transmissions, one providing odd numbered gears and one providing even numbered gears. Shifts between odd numbered gears and even numbered gears can be accomplished without interrupting power flow. While operating in an odd numbered gear, couplers can be actuated to configure the transmission for the next even numbered gear. Dual clutch transmissions have parasitic losses only slightly higher than ASM transmissions.
Motor vehicles, in which the front wheels are the driven wheels and the engine and transmission are located in a forward engine compartment, generally require the engine and transmission to be arranged in a space whose lateral dimension is limited by the spacing between the front wheels. The engine compartments of such vehicles are both narrow and short. When the engine is also of the type having six in-line cylinders, there is an acute need to minimize the package space occupied by the transaxle, particularly its lateral dimension, in order to conserve space for long engines.